Ink jet head and ink jet printer

ABSTRACT

An ink jet head includes a head substrate, a flexible substrate, and a relay substrate. The head substrate includes ink jet elements and a common wiring that extends from an edge of the head substrate and electrically connects in common to the ink jet elements. The flexible substrate is coupled to the head substrate at a first edge and includes a drive circuit, a common connection wiring that extends between the first edge and a second edge opposite the first edge and is electrically connected to the common wiring, and a first reference potential wiring electrically connected to a reference voltage terminal of the drive circuit and disposed separately from the common connection wiring. The flexible substrate includes an output monitor wiring extending from an output terminal of the driver circuit to the second edge through a region between the common connection wiring and the first reference potential wiring.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority fromJapanese Patent Application No. 2018-027578, filed Feb. 20, 2018, theentire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to an ink jet head and anink jet printer.

BACKGROUND

An ink jet head includes a flow path formation member in which aplurality of ink chambers are formed, a nozzle plate on which aplurality of nozzles that communicate with the respective ink chambersare formed, and a head substrate on which a plurality of elements, suchas actuators, corresponding to the ink chambers are arranged.

The head substrate may be connected to a printer control unit via aflexible substrate, a relay substrate, a cable, or the like. A driveintegrated circuit (IC) chip that drives the plurality of elements maybe mounted on the flexible substrate in some cases.

The drive IC chip outputs drive power in accordance with a command fromthe printer control unit and supplies the drive power to the respectiveelements. In this manner, the elements are deformed or caused togenerate heat and thus an ink pressure in a pressure chamber increases,and ink is ejected from the nozzles.

Discrete wirings for supplying drive signals and a common wiring forsupplying a reference potential (ground potential) may be connected tothe respective elements.

The common wiring may be disposed through a different route without theflexible substrate interposed therebetween or is disposed via the driveIC chip on the flexible substrate.

If the common wiring is disposed through a route that is different fromthe flexible substrate, the wiring may become long and complicated. Thismay increase noise or lead to degradation of ejection properties due tovoltage dropping. Also, a wiring connecting operation may becomecumbersome.

If the common wiring is disposed via the drive IC chip on the flexiblesubstrate, improper operations of the drive IC may occur due to noisethat is transmitted through the common wiring. Also, the common wiringmay need to be formed with a thin width, and this may lead todegradation of ejection properties due to voltage dropping. If the widthof the common wiring is increased, an area of the drive IC may increase.

DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are diagrams illustrating a configuration of anelectrical circuit in an ink jet head according to an embodiment, whereFIG. 1A illustrates an example and FIG. 1B illustrates a modificationexample.

FIGS. 2A and 2B are diagrams illustrating an ink jet head according to afirst embodiment, where FIG. 2A illustrates a state before bonding andFIG. 2B illustrates a state after bonding.

FIGS. 3A to 3E are diagrams illustrating the ink jet head according tothe first embodiment, where FIG. 3A illustrates a cross-sectional viewalong A-A in FIG. 2B, FIG. 3B illustrates a cross-sectional view alongB-B in FIG. 2B, FIG. 3C illustrates an enlarged view of a part C in FIG.2B, and FIG. 3D is an enlarged view of a part D in FIG. 2B, and FIG. 3Eis an enlarged view of a part E in FIG. 2B.

FIG. 4 is a diagram illustrating flexible substrates formed in asprocket film.

FIGS. 5A and 5B are diagrams illustrating an ink jet head according to asecond embodiment, where FIG. 5A illustrates a state before bonding andFIG. 5B illustrates a state after bonding.

FIG. 6 is a diagram illustrating flexible substrates formed in asprocket film.

FIG. 7 is a diagram illustrating an ink jet head according to a thirdembodiment.

FIG. 8 is a diagram illustrating flexible substrates formed in asprocket film.

FIG. 9 is a diagram illustrating an ink jet head according to a fourthembodiment.

FIG. 10 illustrates a perspective view of the inkjet head.

FIG. 11 illustrates a partially enlarged view of a front surface of thehead substrate.

FIGS. 12A and 12B are diagrams illustrating enlarged views of ink jetheads, where FIG. 12A illustrates two flexible substrates separated fromeach other, and FIG. 12B illustrates two flexible substrates arranged inthe vicinity of each other.

DETAILED DESCRIPTION

An embodiment is directed to providing an ink jet head and an ink jetprinter without a complicated and thin common wiring on a flexiblesubstrate.

An ink jet head according to an embodiment includes a head substrate, aflexible substrate, and a relay substrate. The head substrate includes,thereon, a plurality of ink jet elements configured to cause ink to beejected from a plurality of nozzles, and a common wiring extending froman edge of the head substrate and electrically connected to the ink jetelements in common. The flexible substrate is coupled to the edge of thehead substrate at a first edge and includes, thereon, a drive ICconfigured to drive the ink jet elements, a common connection wiringextending between the first edge of the flexible substrate and a secondedge of the flexible substrate opposite to the first edge andelectrically connected to the common wiring, and a first referencepotential wiring disposed separately from the common connection wiring,extending from the second edge of the flexible substrate, andelectrically connected to a reference voltage terminal of the drive IC.The flexible substrate includes an output monitor wiring extending froman output terminal of the driver circuit to the second edge through aregion between the common connection wiring and the first referencepotential wiring. The relay substrate is coupled to the second edge ofthe flexible substrate. The relay substrate includes, thereon, a secondreference potential wiring electrically connected to the commonconnection wiring and the first reference potential wiring.

Hereinafter, an ink jet head and an ink jet printer according to certainexample embodiments will be described with reference to drawings. In therespective drawings, the same reference numerals will be used for thesame configurations.

First Embodiment Ink Jet Heads 3

FIGS. 1A and 1B are diagrams illustrating a configuration of electricalcircuits in an ink jet head 3 according to an embodiment, where FIG. 1Aillustrates an example and FIG. 1B illustrates a modification of theFIG. 1A example.

The ink jet printer 1 includes a plurality of ink jet heads 3. The inkjet printer 1 includes an ink supply unit configured to supply ink tothe ink jet heads 3, a medium transport unit configured to transport arecording medium to the ink jet heads 3, a printer control unit, and thelike.

Each ink jet head 3 includes a plurality of actuators 7, a drive IC 8,and the like. The drive IC 8 includes a drive circuit including outputtransistors 8T.

Each of the plurality of actuators 7 has one end connected to a discretewiring 11 and the other connected to a common wiring 16.

The discrete wiring 11 is a wiring that is discretely connected to acorresponding one of the actuators 7 and is connected to the drive IC 8.The common wiring 16 is a shared wiring that is connected to theactuators 7 and is grounded. That is, each actuator 7 is connected to adrive circuit of the drive IC 8 via a different one of the discretewirings 11 and is connected to a reference potential GND (0 V) via theshared common wiring 16.

The drive circuit of the drive IC 8 controls the output transistors 8Tto selectively have a drive potential V1 and a reference potential GND.If the drive circuit of the drive IC 8 controls an output transistor 8Tto have the drive potential V1, the corresponding actuator 7 is changedwith the drive potential V1. If the drive circuit of the drive IC 8controls an output transistor 8T to have the reference potential GND,the corresponding actuator 7 is caused to discharge electricity to reachthe reference potential GND.

FIGS. 2A and 2B are diagrams illustrating an ink jet head 3 according toa first embodiment, where FIG. 2A illustrates a state before bonding andFIG. 2B illustrates a state after bonding. A flexible substrate 20 and arelay substrate 30 are illustrated with wirings and the like in a mannerin which the wirings and the like are seen through the respectivesubstrates, for convenience of explanation.

FIGS. 3A to 3E illustrate diagrams illustrating the ink jet headaccording to the first embodiment, where FIG. 3A illustrates across-sectional view along A-A in FIG. 2B, FIG. 3B illustrates across-sectional view along B-B in FIG. 2B, FIG. 3C illustrates anenlarged view of a part C in FIG. 2B, FIG. 3D illustrates an enlargedview of a part D in FIG. 2B, and FIG. 3E illustrates an enlarged view ofa part E in FIG. 2B. Only the respective wirings are illustrated inFIGS. 3C to 3E for convenience of explanation.

The ink jet head 3 includes a head substrate 10, a flexible substrate20, and a relay substrate 30.

In the head substrate 10, a plurality of actuators 7 corresponding toink chambers, respectively, are arranged. The flexible substrate 20 andthe relay substrate 30 are bonded to the head substrate 10. The relaysubstrate may be referred to as a “print substrate” in some contexts.

In the following description, the longitudinal direction of the headsubstrate 10 will be referred to as X direction or a left-rightdirection. +X direction will be referred to as a right direction, and −Xdirection will be referred to as a left direction. The end in −Xdirection (first terminal) and the end in +X direction (second end) willcollectively be referred to as both ends.

The short side direction of the head substrate 10 will be referred to asY direction or an upper-lower direction. +Y direction will be referredto as an upper direction or an output direction, and −Y direction willbe referred to as a lower direction or an input direction. The thicknessdirection of the head substrate 10 will be referred to as Z direction.+Z direction will be referred to as a front direction, and −Z directionwill be referred to as a rear direction.

In addition, electrical coupling will be referred to as connection, andphysical coupling will be referred to as bonding.

The head substrate 10, the flexible substrate 20, and the relaysubstrate 30 are sequentially bonded to each other in Y direction. Thehead substrate 10 is arranged in +Y direction with respect to twoflexible substrates 20, the relay substrate 30 is arranged in −Ydirection with respect to the two flexible substrates 20. That is, thetwo flexible substrates 20 are bridged in parallel between the headsubstrate 10 and the relay substrate 30.

An edge 20 a on the output side of the flexible substrate 20 overlaps anedge 10 b on the input side of the head substrate 10. An edge 20 b onthe input side of the flexible substrate 20 overlaps an edge 30 a on theoutput side of the relay substrate 30.

Head Substrate 10

FIG. 10 illustrates a perspective view of the inkjet head 3. FIG. 11illustrates a partially enlarged view of a front surface (nozzle plate)10 s of the head substrate 10. The head substrate 10 is a one-sided hardsubstrate made of silicon or glass, and a planar shape thereof is arectangular shape. The head substrate 10 has a plurality of actuators 7.The actuators 7 are piezoelectric elements. The plurality of actuators 7are formed by microelectromechanical systems (MEMS) and are arranged ona front surface 10 s of the head substrate 10. The actuator 7, which isa driving source for ejecting ink, is provided for each nozzle 51. Eachof the actuators 7 is formed in an annular shape, and the actuators 7are arranged so that the nozzles 51 are located at the center thereof.

The plurality of actuators 7 are aligned in parallel in the left-rightdirection. In one implementation, the actuator 7 includes eightactuators 7 arranged in Y axis direction as one set in X axis direction.For example, 150 sets are arranged in X axis direction, and a total of1200 actuators 7 are arranged.

A plurality of nozzles 51 for ejecting ink are arranged on a frontsurface 10 s of the head substrate 10. The nozzles 51 aretwo-dimensionally arranged in the column direction (X direction) and therow direction (Y direction). However, the nozzles 51 arranged in the rowdirection (Y direction) are arranged obliquely so that the nozzles 51 donot overlap on the axis of the Y axis. The ink ejected from each nozzle51 is supplied from the ink supply path 52 communicating with the nozzle51.

In addition, the head substrate 10 has discrete wirings 11 and a commonwiring 16. The discrete wirings 11 and the common wiring 16 areconnected to the actuators 7.

The discrete wirings 11 are disposed in parallel from the respectiveactuators 7 to the edge 10 b on the input side on the front surface 10s. The drive potential V1 or the reference potential GND is supplied tothe discrete wirings 11.

The number of the discrete wirings 11 is the same as the number of theactuators 7. The number of the discrete wirings 11 is 1200, for example.

Wirings extending from the actuators 7 to the common wiring 16 aredisposed in parallel to each other from the respective actuators 7toward the edge 10 a on the output side on the front surface 10 s. Thesewirings connected to the actuators 7 are commonly connected to thecommon wiring 16 at the edge 10 a, and the common wiring 16 is disposedtoward both left and right ends along the edge 10 a. Further, the commonwiring 16 is disposed from both left and right ends of the edge 10 a tothe edge 10 b along the edges 10 c and 10 d on the left and right sides.That is, the common wiring 16 is a single wiring, is disposed along theedges 10 a, 10 c, and 10 d except for the edge 10 b, is further branchedfrom the edge 10 a.

The reference potential GND is supplied to the common wiring 16.

Common wirings 16L and 16R are respectively arranged at both left andright ends at the edge 10 b of the head substrate 10. The plurality ofdiscrete wirings 11 are arranged between the common wirings 16L and 16R.The discrete wirings 11 are divided into two on the left and right sidesof the edge 10 b. For example, 500 discrete wirings 11 are arranged onthe left side, and 500 discrete wirings 11 are arranged on the rightside of the edge 10 b.

Since the discrete wirings 11 are divided into two on the left and rightsides of the edge 10 b, the discrete wirings 11 are disposed so as to beinclined relative to X direction between the actuators 7 and the edge 10b.

The discrete wirings 11 and the common wiring 16 are formed of nickel,aluminum, gold, or an alloy thereof. Since these wirings are formedthrough a semiconductor process, film thicknesses of conductive bodiesare relatively thin. Specifically, line thicknesses of the discretewirings 11 and the common wiring 16 are 0.4 μm (see FIGS. 3A and 3B).

The line width, the wiring interval, and the arrangement interval(pitch) of the discrete wirings 11 are 20 μm, 20 μm, and 40 μm,respectively, at the edge 10 b. The line widths of the common wirings16L and 16R are 0.8 mm (see FIGS. 3C and 3D).

Flexible Substrate 20

The flexible substrate 20 is a one-sided soft substrate made of asynthetic resin film such as polyimide, and a planar shape thereof is arectangular shape. The flexible substrate 20 is also referred to as aflexibility film substrate or a flexible film substrate (flexibleprinted circuit: FPC). A flexible substrate 20L on the left side and aflexible substrate 20R on the right side have the same shape andconfiguration.

Each flexible substrate 20 has a single drive IC 8. The drive IC 8 ismounted on a rear surface 20 t, which is a surface opposite to a frontsurface of the flexible substrate 20 depicted in FIG. 2. The drive IC 8is arranged in the left-right direction at the center of the flexiblesubstrate 20, and the respective terminals are sealed with resin.

Since the flexible substrate 20 can be considered as a package of thedrive IC 8, a sealed state in which the drive IC 8 is mounted on theflexible substrate 20 is also referred to as a tape carrier package(TCP) or a chip-on-film (COF) package.

In addition, each flexible substrate 20 has output wirings 21, inputwirings 22, a power source wiring 23, aground wiring 24, output monitorwirings 25, and common connection wirings 26.

The wirings except for the common connection wirings 26 are connected tothe drive IC 8. That is, the output wirings 21, the input wirings 22,the power source wiring 23, the ground wiring 24, and the output monitorwirings 25 are connected to the drive IC 8.

Meanwhile, the common connection wirings 26 are independently disposedwithout being connected to the drive IC 8 and the other wirings.

The output wirings 21 are disposed in parallel to each other from thedrive IC 8 to the edge 20 a on the output side on the rear surface 20 t.The output wirings 21 are respectively connected to a plurality ofoutput terminals provided on the rear surface of the drive IC 8. Thedrive potential V1 or the reference potential GND is supplied to theoutput wirings 21.

The number of output wirings 21 is one half of the number of thediscrete wirings 11. The number of the output wirings 21 is 600, forexample.

The input wirings 22 are disposed in parallel to each other from thedrive IC 8 to the edge 20 b on the input side on the rear surface 20 t.The input wirings 22 are respectively connected to a plurality of inputterminals that are provided on the rear surface of the drive IC 8. Acontrol signal is supplied to the input wirings 22.

The number of input wirings 22 is smaller than the number of the outputwirings 21. The number of the input wirings 22 is 50, for example.

The power source wiring 23 and the ground wiring 24 are wirings that arearranged in such a manner in which these wirings travel across a regionon which the drive IC 8 is mounted, in the left-right direction, arebent at a substantially right angle on both left and right ends, and aredisposed in parallel to each other. That is, the power source wiring 23and the ground wiring 24 are disposed to surround the output side andboth left and right sides of the input wiring 22.

The power source wiring 23 is connected to a plurality of power sourceterminals that are provided on the rear surface of the drive IC 8. Thedrive potential V1 is supplied to the power source wiring 23.

The ground wiring (first reference potential wiring) 24 is connected toa plurality of ground terminals that are provided on the rear surface ofthe drive IC 8. The reference potential GND is supplied to the groundwiring 24.

The number of the power source wirings 23 is one, and the number of theground wirings 24 is one. The power source wiring 23 is arranged on theoutput side and the left and right outer sides, and the ground wiring 24is arranged on the input side and the left and right inner sides.

The output monitor wirings 25 are two wirings that are disposed from thedrive IC 8 to the edge 20 b on the input side. The output monitorwirings 25 may be connected to any of a plurality of output terminalsthat are provided on the rear surface of the drive IC 8. That is, theoutput monitor wirings 25 may be connected to any of the plurality ofoutput wirings 21. Drive waveforms that are changed between the drivepotential V1 and the reference potential GND by the drive IC 8 aresupplied to the output monitor wirings 25.

One output monitor wiring 25 is arranged on each of the left and rightsides. Each output monitor wiring 25 is extracted from ends of theoutput wirings 21, is directed from the region on which the drive IC 8is mounted to both left and right ends, is bent at a right angle, and isdisposed to reach the edge 20 b. The output monitor wirings 25 arearranged on the output side and the left and right outer sides of thepower source wiring 23 and are disposed in parallel to the power sourcewiring 23.

The common connection wirings 26 are two wirings disposed in theupper-lower direction along the left and right edges 20 c and 20 d onthe rear surface 20 t. That is, a common connection wiring 26L isarranged on the leftmost edge while a common connection wiring 26R isarranged on the rightmost edge. The common connection wirings 26L and26R are disposed to directly connect the edge 20 b and the edge 20 awithout being connected to the drive IC 8 and the like. The referencepotential GND is supplied to the common connection wirings 26.

The ground wiring 24 and the common connection wirings 26 are separatefrom each other. In other words, the ground wiring 24 and the commonconnection wirings 26 are independently connected to the relay substrate30 and are electrically connected to each other on the relay substrate30.

A plurality of input wirings 22 are aligned at the edge 20 b of theflexible substrate 20, the ground wiring 24 is disposed outside theplurality of input wirings 22, and the power source wiring 23 isdisposed further outside the ground wiring 24. Since the flexiblesubstrate 20 is a one-sided substrate, wirings on the flexible substratecannot cross the other wirings.

Basically, since the common connection wirings 26 and the drive IC 8 areseparate from each other on the flexible substrate 20, it is possible todispose the route of the output monitor wirings 25 to start from any ofthe output wirings 21, pass between the common connection wirings 26 andthe power source wiring 23, and reach the edge 20 b without crossing theother wirings.

Note that the embodiment is not limited to a case in which the powersource wiring 23 is disposed outside the ground wiring 24, and theground wiring 24 may be disposed outside the power source wiring 23 insome cases.

The output wirings 21, the input wirings 22, the power source wiring 23,the ground wiring 24, the output monitor wirings 25, and the commonconnection wirings 26 are formed of copper. These wirings are formed byusing an adhesive on a polyimide film or by performing electrolyticlamination and then performing patterning thereon. Therefore, theconductive body thicknesses are thicker than those of the respectivewirings (the discrete wirings 11 and the common wiring 16) on the headsubstrate 10. The line thicknesses of the respective wirings from theoutput wirings 21 to the common connection wirings 26 are 8 μm (seeFIGS. 3A and 3B).

At the edge 20 a, the arrangement interval (pitch) of the output wirings21 is 40 μm, which is the same as that of the discrete wirings 11. Theline width of the output wirings 21 is 18 μm, which is smaller than thatof the discrete wirings 11. The wiring interval of the output wirings 21is 22 μm, which is greater than that of the discrete wirings 11 (seeFIG. 3D).

Since the conductive bodies (the respective wirings) on the flexiblesubstrate 20 have thicknesses that are about twenty times larger thanthose of the conductive bodies on the head substrate 10, sheetresistance is substantially lower than that of the conductive bodies onthe head substrate 10. If the widths (line widths) of the conductivebodies on the head substrate 10 with the high sheet resistance arereduced, wiring resistance significantly increases. Meanwhile, anincrease in resistance is relatively small even if the widths (linewidths) of the conductive bodies on the flexible substrate 20 with lowsheet resistance are reduced. By reducing the widths of the conductivebodies of the output wirings 21 on the polyimide film side, which isrelatively less influenced by the increase in resistance even if thewidths of the conductive bodies are narrowed, to 18 μm and setting awiring interval to be as large as 22 μm corresponding to the narrowedwidth, the increase in resistance is suppressed, and insulating defectsare prevented even if deviation occurs during connection.

The line width of the common connection wiring 26 is 0.4 mm, which is ahalf of those of the common wirings 16L and 16R (see FIG. 3C).

Since the thicknesses of the conductive bodies (the respective wirings)on the flexible substrate 20 are about twenty times as thick as those ofthe conductive bodies on the head substrate 10, sheet resistance issufficiently lower than that of the conductive bodies on the headsubstrate 10. If the widths (line widths) of the conductive bodies onthe head substrate 10 with high sheet resistance is reduced, wiringresistance significantly increases. Meanwhile, an increase in resistanceis relatively small even if the widths (line widths) of the conductivebodies on the flexible substrate 20 with low sheet resistance arereduced. By setting the width of the conductive body of the commonconnection wiring 26 on the polyimide film side, which is relativelyless influenced by the increase in the resistance even if the width ofthe conductive body is reduced, to 0.4 mm, it is possible to suppressthe increase in resistance and also to suppress the length of thepolyimide film in X direction. In this manner, it is possible to improveoperability in bonding between the flexible substrate 20 and the headsubstrate 10, to suppress manufacturing costs, and to suppress filmcosts.

The common connection wirings 26L and 26R are arranged at both left andright ends at the edge 20 a of the flexible substrate 20. The pluralityof output wirings 21 are arranged at the center of the edge 20 a.

In this manner, if the flexible substrate 20L is bonded to the left sideof the edge 10 b of the head substrate 10, the common connection wiring26L is connected to the common wiring 16L, and the output wirings 21 arerespectively connected to the discrete wirings 11 (connectionlocations). The common connection wiring 26R of the flexible substrate20L may not be connected to any wirings of the head substrate 10 and therelay substrate 30, and therefore may be referred to as a dummy wiring.

If the flexible substrate 20R is bonded to the right side of the edge 10b of the head substrate 10, the common connection wiring 26R isconnected to the common wiring 16R, and the output wirings 21 arerespectively connected to the discrete wirings 11 (connectionlocations). The common connection wiring 26L of the flexible substrate20L may not be connected to any wirings of the head substrate 10 and therelay substrate 30, and therefore may be referred to as a dummy wiring.

The flexible substrate 20 and the head substrate 10 are connected via ananisotropic conductive film (ACF). The ACF is arranged between the edge20 a of the rear surface 20 t of the flexible substrate 20 and the edge10 b of the front surface 10 s of the head substrate 10.

If the flexible substrate 20 and the head substrate 10 are thermallypress-fitted to each other with a heater or the like with the ACFinterposed therebetween, the flexible substrate 20 and the headsubstrate 10 can be bonded to each other, and therefore, the respectivewirings can be electrically connected to each other. For example, thecommon wirings 16L and 16R and the common connection wirings 26L of theflexible substrate 20L and 26R of the flexible substrate 20R areelectrically connected to each other.

In a case in which stretching of the flexible substrate during thethermal pressing cannot be ignored, the arrangement interval (pitch) maybe formed to be narrower than 40 μm in a state before the connectionsuch that the arrangement interval (pitch) after the connection becomes40 μm.

The common connection wirings 26L and 26R are arranged at both left andright ends at the edge 20 b of the flexible substrate 20. A plurality ofinput wirings 22 are arranged at the center of the edge 20 b. Further,the output monitor wiring 25, the power source wiring 23, and the groundwiring 24 are arranged between the common connection wiring 26L and theinput wirings 22. Similarly, the output monitor wiring 25, the powersource wiring 23, and the ground wiring 24 are arranged between thecommon connection wiring 26R and the input wirings 22.

At the edge 20 b, the line width, the wiring interval, and thearrangement interval (pitch) of the input wirings 22 are 0.15 mm, 0.15mm, and 0.3 mm, respectively (see FIG. 3E). The line width of the outputmonitor wirings 25 is 100 μm. The line widths of the power source wiring23, the ground wiring 24, and the common connection wiring 26 are 0.4mm.

Relay Substrate 30

The relay substrate 30 is a hard multilayered substrate in which epoxyresin layers with glass fibers and copper wiring layers are laminated,and a planar shape thereof is a rectangular shape. The relay substrate30 may be a printed circuit board or the like.

The relay substrate 30 has electronic parts and a connector disposedand/or formed thereon. The relay substrate 30 has input wirings 32,power source wirings 33, ground wirings 34, and output monitor wirings35.

The input wirings 32, the power source wirings 33, and the groundwirings 34 are connected to the connector.

The output monitor wiring 35 is connected to a monitor pin 37 thatextends from a front surface 30 s of the relay substrate 30.

The input wirings 32 are a plurality of wirings that are disposed inparallel to each other from the edge 30 a on the output side toward theconnector. The input wirings 32 are exposed on the front surface 30 s atthe edge 30 a and are arranged inside the layers at locations other thanthe edge 30 a.

The number of input wirings 32 is the same as the number of inputwirings 22 (for example, 50×2).

A control signal for the drive IC 8 is supplied from a printer controlunit to the input wirings 32 via serial communication. That is, acontrol signal for controlling the actuators 7 is input from the printercontrol unit to the input wirings 32 via the connector or the like.

The power source wirings 33 and the ground wirings 34 are wirings thatare disposed in parallel to each other from the edge 30 a toward theconnector. The power source wirings 33 are exposed on the front surface30 s at the edge 30 a and are arranged inside the layers at locationsother than the edge 30 a. The ground wiring (second reference potentialwiring) 34 is exposed on the front surface 30 s at the edge 30 a.

The power source wirings 33 are branched into four at the edge 30 a. Twopower source wirings 33 are arranged on the left side of the edge 30 a,and two power source wirings 33 are arranged on the right side thereof.

The drive potential V1 for driving the actuators 7 is supplied from apower source unit (see FIG. 2B) to the power source wirings 33 via theconnector or the like.

The ground wirings 34 are branched into six at the edge 30 a. Two groundwirings 34 are arranged on the left side of the edge 30 a, and twoground wirings 34 are arranged on the right side thereof. Further, oneground wiring 34 is arranged at each of both left and right ends of theedge 30 a (ground wirings 34L and 34R).

The two ground wirings 34 are disposed in parallel to each other on aninner side of the two power source wirings 33 on left and right sides ofthe edge 30 a. The ground wirings 34L and 34R are disposed in parallelto each other on an outer side of the power source wirings 33 at bothleft and right sides of the edge 30 a.

The reference potential GND that causes the actuators 7 to dischargeelectricity is supplied from the power source unit to the ground wirings34 via the connector.

The output monitor wirings 35 are four wirings that are disposed fromthe edge 30 a to the four monitor pins 37. The four monitor pins 37 arearranged at arbitrary locations on the front surface 30 s of the relaysubstrate 30. A necessity of adjusting drive waveforms in accordancewith ink properties occurs in the ink jet head 3 in some cases. In thosecases, it is possible to connect a measurement device such as anoscilloscope to the four monitor pins 37 and to check the drivewaveforms.

The output monitor wirings 35 are exposed on the front surface 30 s atthe edge 30 a and are arranged inside the layers at locations other thanthe edge 30 a.

The output monitor wirings 35 are disposed on an outer side of the powersource wirings 33 at the edge 30 a. The two output monitor wirings 35are arranged in parallel to each other at the center of the edge 30 a.The output monitor wirings 35 are disposed in parallel to each otherbetween the ground wirings 34L and 34R and the power source wirings 33at both left and right ends of the edge 30 a.

The input wirings 32, the power source wirings 33, the ground wirings34, and the output monitor wirings 35 are formed of copper. The linethicknesses of the respective wirings from the input wirings 32 to theoutput monitor wirings 35 are 35 μm (see FIGS. 3A and 3B). The linethicknesses of the conductive bodies (the respective wirings) on therelay substrate 30 are thicker than those of the conductive bodies onthe flexible substrate 20.

At the edge 30 a, the arrangement interval (pitch) of the input wirings32 is 0.3 mm, which is the same as that of the input wirings 22. Theline width of the input wirings 32 is 0.1 mm, which is smaller than thatof the input wirings 22. The interval of the input wirings 32 is 0.2 mm,which is larger than that of the input wirings 22 (see FIG. 3E).

Since the thicknesses of the conductive bodies (the respective wirings)on the relay substrate 30 are about 4 times as thick as those of theconductive bodies on the flexible substrate 20, sheet resistance islower than that of the wirings on the head substrate 10. Therefore, anincrease in resistance is relatively small even if the widths (linewidths) of the conductive body on the relay substrate 30 are reduced.

The width of the input wirings 32 on the side of the relay substrate,which is relatively less influenced by the increase in resistance evenif the widths of the conductive bodies are reduced, is set to 0.1 mm,which is narrower than 0.15 mm, which is the width of the conductivebodies of the input wirings 22. By setting the wiring interval to be aswide as 0.2 mm corresponding to the reduction in width of the inputwirings 32, the increase in resistance is suppressed, and insulatingdefects are prevented even if deviation occurs during connection.

That is, this is similar to the aforementioned relationship between thediscrete wirings 11 on the head substrate 10 and the output wirings 21on the flexible substrate 20.

When two wiring substrates with different sheet resistance are connectedto each other, the line width and the wiring interval of the firstwirings on the first wiring substrate on the side of high sheetresistance are set to 1:1, and the line width of second wirings on thesecond wiring substrate on the side of low sheet resistance is set to benarrower than the wiring interval thereof even if the pitch thereof isthe same as that of the first wirings. In this manner, it is possible tosuppress an increase in resistance and to achieve connection that isless likely to cause insulating defects even if deviation occurs duringthe connection.

The line widths of the power source wirings 33 and the ground wirings 34are 0.4 mm at the edge 30 a. The line width of the output monitorwirings 35 is 100 μm.

At the edge 30 a of the relay substrate 30, the ground wiring 34L, theoutput monitor wiring 35, the power source wiring 33, the ground wiring34, the plurality of input wirings 32, the ground wiring 34, the powersource wiring 33, and the output monitor wiring 35 are arranged in thisorder from the left side to the center.

At the edge 30 a of the relay substrate 30, the ground wiring 34R, theoutput monitor wiring 35, the power source wiring 33, the ground wiring34, the plurality of input wirings 32, the ground wiring 34, the powersource wiring 33, and the output monitor wiring 35 are arranged in thisorder from the right side to the center.

In this manner, if the flexible substrate 20L is bonded to the left sideof the edge 30 a of the relay substrate 30, the respective wirings areconnected to each other. That is, the input wirings 32 are connected tothe input wirings 22, the power source wirings 33 are connected to thepower source wiring 23, the ground wirings 34 are connected to theground wiring 24, and the output monitor wirings 35 are connected to theoutput monitor wirings 25. The ground wiring 34L is respectivelyconnected to the common connection wiring 26L on the flexible substrate20L.

If the flexible substrate 20R is bonded to the right side of the edge 30a of the relay substrate 30, the respective wirings are connected toeach other. That is, the input wirings 32 are connected to the inputwirings 22, the power source wirings 33 are connected to the powersource wiring 23, the ground wirings 34 are connected to the groundwiring 24, and the output monitor wirings 35 are connected to the outputmonitor wirings 25. The ground wiring 34R is respectively connected tothe common connection wiring 26R on the flexible substrate 20R.

The relay substrate 30 and the two flexible substrates 20 are connectedto each other via an ACF. The ACF is arranged between the edge 30 a ofthe front surface 30 s of the relay substrate 30 and the edge 20 b ofthe rear surface 20 t of the flexible substrate 20.

If the edge 30 a of the relay substrate 30 and the edge 20 b of theflexible substrate 20 are thermally press-fitted by a heater or the likewith the ACF interposed therebetween, the relay substrate 30 and the twoflexible substrates 20 can be bonded to each other, and further, therespective wirings can be electrically connected to each other. Forexample, the common connection wirings 26L and 26R and the groundwirings 34L and 34R are electrically connected to each other.

FIG. 4 is a diagram illustrating the flexible substrates 20 formed on asprocket film F. The flexible substrates 20 are illustrated in such amanner in which the flexible substrates 20 are seen through a syntheticresin film.

A plurality of flexible substrates 20 are continuously formed on thesprocket film F, which is made of a synthetic resin such as polyimide.This plurality of flexible substrates 20 thus formed are transported toan assembling plant or the like for ink jet heads 3. These flexiblesubstrates can be transported while still in the sprocket film F state.

When the individual flexible substrates 20 are cut out of the sprocketfilm F, outer perimeters (depicted as a broken line in FIG. 4) of theflexible substrates 20 are cut. In this manner, the flexible substrates20 (20L and 20R) can be bonded to the head substrate 10 and the like.

In this manner, the ink jet head 3 can avoid complicated and thin commonwirings (e.g., the ground wiring 24 and the common connection wiring 26)on the flexible substrates 20. Therefore, it is possible to manufacturethe ink jet printer 1 that is less influenced by noise and can preventdegradation of ejection properties.

As described above, the line thickness (the thickness of the conductivebody) of the common wiring 16 formed on the head substrate 10 of the inkjet head 3 is 0.4 μm, which is significantly thin. Since drive currentsfor all the actuators 7 are collected at the common wiring 16 unlike thediscrete wirings 11, a large current flows therethrough. For thatreason, the common wiring 16 requires a line width (the width of theconductive body) that is about 80 times as thick as that of the discretewirings 11. In the present embodiment, two common wirings 16 with theline width of 0.8 mm are arranged at the edge 10 b.

The line thickness of the common connection wiring 26 formed on theflexible substrate 20 is 8 μm, which is the thickness that is 20 timesas thick as that of the common wiring 16. Since the cross-sectional areaof the common connection wiring 26 is large even if the line widththereof is a half (0.4 mm) of the line width (0.8 mm) of the commonwiring 16, the common connection wiring 26 has sufficiently low electricresistance.

If positional deviations in the left-right direction occur in thebonding between the head substrate 10 and the flexible substrates 20,there is a concern that a part of the common wiring 16 and a part of thecommon connection wiring 26 are connected to each other and the electricresistance at the connection location increases.

If the electric resistance at the connection location between the commonwiring 16 and the common connection wiring 26 is high, a drive voltageof the actuators 7 drops, and stability of ink ejection deteriorates, orthe common wiring 16 generates heat, and durability deteriorates.

In the ink jet head 3, the common wiring 16 with a large line width andthe common connection wiring 26 with a small line width are connected toeach other in an overlapping manner. For that reason, the commonconnection wiring 26 is reliably arranged within a range of the linewidth of the common wiring 16. Since the common wiring 16 of aconductive body with a small sectional area and with high (or equal)electric resistance is completely connected to the common connectionwiring 26 of a conductive body with a large sectional area and with lowelectric resistance, it is possible to avoid an increase in the electricresistance at the connection location.

Therefore, positioning precision for bonding the head substrate 10 andthe flexible substrates 20 does not increase, and it is possible toeasily perform the bonding.

In the ink jet head 3, the ground wirings 34L and 34R that supply thereference potential GND only to the actuators 7 are disposed on therelay substrate 30. According to this configuration, it is possible toprovide switches or the like for the ground wirings 34L and 34R and toarbitrarily control the reference potential to be supplied to theactuator 7.

As illustrated in FIG. 1B, for example, it is possible to supply anegative potential V2 to the actuators 7 by switching the switches. Inthis manner, it is possible to perform polling processing on theactuators 7.

It is also possible to make the potential of the common wiring 16different from the Gnd potential, variable and to adjust a bias voltageto be applied to the actuators 7.

In the ink jet head 3, the common connection wiring 26 that supplies thereference potential to the actuators 7 and the ground wiring 24 thatsupplies the reference potential to the drive IC 8 are separately andindependently provided on the flexible substrate 20. According to thisconfiguration, it is possible to dispose the output monitor wirings 25between the output wirings 21 of the drive IC 8 and the commonconnection wiring 26. The output monitor wirings 25 are connected to anyof the plurality of output terminals of the drive IC 8 and are connectedto the output monitor wirings 35 on the relay substrate 30.

According to this connection, it is possible to check output waveformsof the drive IC 8 on the relay substrate 30. In other words, it is notnecessary to check the output waveforms of the drive IC 8 on theflexible substrates 20 as in the related art.

Therefore, it is possible to easily check the output waveforms of thedrive IC 8 when the ink jet head 3 is developed or malfunction thereofis analyzed.

Second Embodiment Ink Jet Head 4

FIGS. 5A and 5B are diagrams illustrating an inkjet head 4 according toa second embodiment, where FIG. 5A illustrates a state before bondingand FIG. 5B illustrates a state after bonding. Wirings and the like onflexible substrates 40 and a relay substrate 30 are illustrated in sucha manner in which the wirings and the like are seen through thesubstrates for convenience of explanation.

The same reference numerals will be used for the same aspects and thelike as those in the ink jet head 3 according to the first embodiment,and repeated description thereof is omitted.

The ink jet head 4 includes a head substrate 10, the flexible substrates40, and the relay substrate 30. Two flexible substrates 40 are bridgedin parallel to each other between the head substrate 10 and the relaysubstrate 30.

Flexible Substrate 40

The flexible substrates 40 have substantially the same configuration asthat of the flexible substrates 20.

A flexible substrate 40L on the left side does not have the commonconnection wiring 26R, and a flexible substrate 40R on the right sidedoes not have the common connection wiring 26L. That is, the flexiblesubstrate 40L is obtained by removing the common connection wiring 26Rfrom the flexible substrates 20, and the flexible substrate 40R isobtained by removing the common connection wiring 26L from the flexiblesubstrates 20.

FIG. 6 is a diagram illustrating the flexible substrates 40 formed in asprocket film F. The flexible substrates 40 are illustrated in a mannerin which the flexible substrate 40 is seen through a synthetic resinfilm for convenience of explanation.

The flexible substrates 40 are formed continuously on the sprocket filmF made. This plurality of flexible substrates 40 is transported to anassembling plant while still in a sprocket film F state.

The flexible substrates 40 formed on the sprocket film F havesubstantially the same configuration as that of the flexible substrates20 according to the first embodiment. That is, the flexible substrates40 formed on the sprocket film F have two common connection wirings 26.

When the individual flexible substrates 40R are cut from the sprocketfilm F, the common connection wirings 26L are left in the sprocket filmF (the broken line in FIG. 6). That is, the common connection wirings26L are separated from the flexible substrates 40. In this manner, itbecomes possible to bond each flexible substrate 40R to the headsubstrate 10 or the like.

When the individual flexible substrates 40L are cut from the sprocketfilm F, the common connection wirings 26R are left in the sprocket filmF (the broken line in FIG. 6). That is, the common connection wirings26R are separated from the flexible substrates 40. In this manner, itbecomes possible to bond each flexible substrate 40L to the headsubstrate 10 or the like.

The ink jet head 4 provides effects and advantages that are similar tothose of the ink jet head 3. That is, it is possible to avoidcomplicated and thin common wirings (the ground wiring 24 and the commonconnection wirings 26) on the flexible substrate 40 on which the driveIC 8 for driving the actuators 7 is mounted. Therefore, it is possibleto provide the ink jet printer 1 capable of preventing degradation ofejection properties.

Further, the ink jet head 4 can improve manufacturing efficiency. Thatis, cut lines are differentiated when the individual flexible substrates40 are cut from the sprocket film F. In this manner, it is possible tocut the flexible substrates 40L and 40R from the sprocket film F onwhich the plurality of flexible substrates 40 with the sameconfiguration are formed.

Since it is only necessary to differentiate the cut lines, themanufacturing efficiency can be improved. Since it is not necessary tomanufacture a plurality of types of substrates, it is possible to reducecosts.

As described above, the flexible substrate 40L does not have the commonconnection wiring 26R, and the flexible substrate 40R on the right sidedoes not have the common connection wiring 26L in the ink jet head 4.For that reason, the widths of the two flexible substrates 40 decreaseas compared with the first embodiment.

According to this configuration, it is possible to arrange the pluralityof discrete wirings 11, which are divided into two on the left and rightsides, near the center on the head substrate 10. That is, it is possibleto form the direction in which the discrete wirings 11 are disposed toconform to the upper-lower direction.

If the discrete wirings 11 are disposed such that the discrete wirings11 are inclined relative to X direction, electric resistance of therespective discrete wirings 11 would become nonuniform, and insulatingreliability would deteriorate. Further, this may become a factor oflowering a yield of the head substrate 10.

FIGS. 12A and 12B are diagrams illustrating enlarged views of ink jetheads, where FIG. 12A illustrates two flexible substrates separated fromeach other, and FIG. 12B illustrates two flexible substrates arranged inthe vicinity of each other.

According to the ink jet head 4, it is possible to decrease aninclination of the discrete wirings 11 at a center region correspondingto a space between the two flexible substrate 40 by arranging the twoflexible substrates 40 in the vicinity of each other in the left-rightdirection as in FIG. 12B as opposed to that shown in FIG. 12A. It ispossible to form the discrete wirings 11 along X direction. As a result,the electric resistance of the respective discrete wirings 11 becomesuniform, the insulating reliability can be improved, and the yield ofthe head substrate 10 can be improved.

Third Embodiment Ink Jet Head 5

FIG. 7 is a diagram illustrating an ink jet head 5 according to a thirdembodiment. Wirings and the like on flexible substrates 40 and a relaysubstrate 30 are illustrated in such a manner in which the wirings andthe like are seen through the substrates for convenience of explanation.

The same reference numerals will be used for the same members and thelike as those in the ink jet heads 3 and 4 according to the first andsecond embodiments, and repeated description thereof will be omitted.

The ink jet head 5 includes a head substrate 10, the flexible substrates40, and the relay substrate 30. Three flexible substrates 40L, 40C, and40R are bridged in parallel to each other between the head substrate 10and the relay substrate 30.

Flexible Substrate 40

The flexible substrate 40L on the left side does not have the commonconnection wiring 26R, and the flexible substrate 40R on the right sidedoes not have the common connection wiring 26L. The flexible substrate40C at the center does not have the common connection wiring 26. Thatis, the flexible substrate 40C is obtained by cutting two commonconnection wirings 26 from the flexible substrate 20.

FIG. 8 is a diagram illustrating the flexible substrates 40 formed in asprocket film F. The flexible substrates 40 are illustrated in such amanner in which the flexible substrates 40 are seen through a syntheticresin film for convenience of explanation.

The flexible substrates 40 are formed continuously in the sprocket filmF. The flexible substrates 40 formed on the sprocket film F have twocommon connection wirings 26.

When the individual flexible substrates 40R are cut out of the sprocketfilm F, the common connection wirings 26L are left in the sprocket filmF (the broken line in FIG. 8). The common connection wirings 26L areremoved from the flexible substrates 40. As a result, it becomespossible to bond each flexible substrate 40R to the head substrate 10 orthe like.

When the individual flexible substrates 40C are cut out of the sprocketfilm F, the common connection wirings 26L and 26R are left in thesprocket film F (the broken line in FIG. 8). The common connectionwirings 26L and 26R are removed from the flexible substrates 40. As aresult, it becomes possible to bond each flexible substrate 40C to thehead substrate 10 or the like.

When the individual flexible substrates 40L are cut out of the sprocketfilm F, the common connection wirings 26R are left in the sprocket filmF (the broken line in FIG. 8). The common connection wirings 26R areremoved from the flexible substrate 40. As a result, it becomes possibleto bond each flexible substrate 40L to the head substrate 10 or thelike.

The ink jet head 5 provides similar effects and advantages as those ofthe ink jet heads 3 and 4. That is, it is possible to avoid complicatedand thin common wirings (the ground wiring 24 and the common connectionwiring 26) on the flexible substrate 40 on which the drive IC 8 fordriving the actuators 7 is mounted. Therefore, it is possible to providethe ink jet printer 1 that is less influenced by noise and is capable ofpreventing degradation of ejection properties.

Further, the ink jet head 5 can improve manufacturing efficiencysimilarly to the inkjet head 4. That is, cut lines are differentiatedwhen the individual flexible substrates 40 are cut from the sprocketfilm F. In this manner, it is possible to cut the flexible substrates40L, 40C, and 40R from the sprocket film F in which the plurality offlexible substrates 40 with the same configuration are formed.

Since it is only necessary to differentiate the cut lines, themanufacturing efficiency is improved. Since it is not necessary tomanufacture a plurality of types of substrates, it is possible to reducecosts.

In the ink jet head 5, the flexible substrate 40L does not have thecommon connection wiring 26R, the flexible substrate 40R on the rightside does not have the common connection wiring 26L, and the flexiblesubstrate 40C does not have the common connection wiring 26.

According to this configuration, it is possible to form the discretewirings 11 along the upper-lower direction similarly to the ink jet head5. As a result, electric resistance of the respective discrete wirings11 becomes uniform, insulating reliability can be improved, and it ispossible to improve a yield of the head substrate 10.

Fourth Embodiment Ink Jet Head 6

FIG. 9 is a diagram illustrating an ink jet head 6 according to a fourthembodiment. Wirings and the like on a flexible substrate 20 and a relaysubstrate 30 are illustrated in such a manner in which the wirings andthe like are seen through the substrates for convenience of explanation.

The same reference numerals will be used for the same aspects and thelike as those in the ink jet heads 3 to 5 according to the first tothird embodiments, and repeated description thereof will be omitted.

The ink jet head 6 includes a head substrate 10, the flexible substrate20, and the relay substrate 30. A single flexible substrate 20 isbridged between the head substrate 10 and the relay substrate 30.

The ink jet head 6 provides similar effects and advantages as those ofthe ink jet heads 3 to 5. That is, it is possible to avoid complicatedand thin common wirings (the ground wiring 24 and the common connectionwiring 26) on the flexible substrate 20 on which the drive IC 8 fordriving the actuators 7 is mounted. Therefore, it is possible to providethe ink jet printer 1 that is less influenced by noise and is capable ofpreventing degradation of ejection properties.

In the aforementioned respective embodiments, the monitor terminals arenot limited to the monitor pins 37. The monitor terminals may be variousterminals or test points (a part of the output monitor wirings 35).

The aforementioned respective embodiments are not limited to the case inwhich a single drive IC 8 is mounted on a single flexible substrate. Twoor more drive ICs 8 may be mounted on a single flexible substrate. Inthis case, the two or more drive ICs 8 may be arranged in series in theleft-right direction.

The elements that cause the nozzles to eject ink are not limited to theactuators 7 formed by the piezoelectric elements. The elements may beheaters or solenoid valves.

The shape of each substrate is not limited to the rectangular shape andmay be a parallelogram, a trapezoid, or the like. The respective wiringsare not limited to the case in which the wirings are disposed linearlyor in parallel, and various modifications can be made as needed.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the present disclosure. Indeed, the novel embodiments describedherein may be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of thepresent disclosure. The accompanying claims and their equivalents areintended to cover such forms or modifications as would fall within thescope and spirit of the present disclosure.

What is claimed is:
 1. An ink jet head comprising: a head substrateincluding thereon: a plurality of ink jet elements configured to causeink to be ejected from a plurality of nozzles; and a common wiringextending from an edge of the head substrate and electrically connectedin common to the ink jet elements; a flexible substrate having a firstedge coupled to the edge of the head substrate and including thereon: adrive circuit configured to drive the ink jet elements; a commonconnection wiring extending between the first edge and a second edge ofthe flexible substrate opposite the first edge and electricallyconnected to the common wiring; a first reference potential wiringdisposed separately from the common connection wiring, extending fromthe second edge of the flexible substrate, and electrically connected toa reference voltage terminal of the drive circuit; and an output monitorwiring extending from an output terminal of the drive circuit to thesecond edge of the flexible substrate through a region between thecommon connection wiring and the first reference potential wiring; and arelay substrate coupled to the second edge of the flexible substrate andhaving a second reference potential wiring thereon, the second referencepotential wiring being electrically connected to the common connectionwiring and the first reference potential wiring.
 2. The ink jet headaccording to claim 1, wherein the relay substrate further includes: asecond output monitor wiring electrically connected to the outputmonitor wiring.
 3. The ink jet head according to claim 1, whereinwirings are formed on only one surface of the flexible substrate.
 4. Theink jet head according to claim 1, further comprising: a power supplywiring on the flexible substrate, the power supply wiring connected to apower supply terminal of the drive circuit.
 5. The ink jet headaccording to claim 1, wherein the common connection wiring is formedalong a third edge of the flexible substrate that is alignedperpendicular to the first and second edges.
 6. The ink jet headaccording to claim 5, further comprising: a dummy wiring on the flexiblesubstrate, the dummy wiring disposed separately from the first referencepotential wiring and extending between the first and second edges of theflexible substrate along a fourth edge of the flexible substrateopposite the third edge.
 7. The ink jet head according to claim 6,wherein the dummy wiring is electrically isolated from any wiring on thehead substrate and any wiring on the relay substrate.
 8. The ink jethead according to claim 6, wherein the common connection wiring and thedummy wiring are disposed symmetrically with respect to a center line ofthe flexible substrate extending between the first and second edges. 9.The ink jet head according to claim 6, further comprising: a powersupply wiring on the flexible substrate has and having a portionextending between the dummy wiring and the first reference potentialwiring and being connected to a power supply terminal of the drivecircuit.
 10. The ink jet head according to claim 5, further comprising:a second common connection wiring on the flexible substrate, the secondcommon connection wiring disposed separately from the first referencepotential wiring and extending between the first and second edges of theflexible substrate along a fourth edge of the flexible substrateopposite the third edge, the second common connection wiring beingelectrically connected to the common wiring and the second referencepotential wiring.
 11. An ink jet printer comprising: an ink jet head; anink supply device configured to supply ink to the ink jet head; and aconveying device configured to convey a print medium toward the ink jethead, wherein the ink jet head comprises: a head substrate includingthereon: a plurality of ink jet elements configured to cause ink to beejected from a plurality of nozzles; and a common wiring extending froman edge of the head substrate and electrically connected in common tothe ink jet elements; a flexible substrate having a first edge coupledto the edge of the head substrate and including thereon: a drive circuitconfigured to drive the ink jet elements; a common connection wiringextending between the first edge of the flexible substrate and a secondedge of the flexible substrate opposite the first edge and electricallyconnected to the common wiring; a first reference potential wiringdisposed separately from the common connection wiring, extending fromthe second edge of the flexible substrate, and electrically connected toa reference voltage terminal of the drive circuit; and an output monitorwiring extending from an output terminal of the drive circuit to thesecond edge of the flexible substrate through a region between thecommon connection wiring and the first reference potential wiring; and arelay substrate coupled to the second edge of the flexible substrate andhaving a second reference potential wiring thereon, the second referencepotential wiring being electrically connected to the common connectionwiring and the first reference potential wiring.
 12. The ink jet printeraccording to claim 11, wherein the relay substrate further includes: asecond output monitor wiring electrically connected to the outputmonitor wiring.
 13. The ink jet printer according to claim 11, whereinwirings are formed on only one surface of the flexible substrate. 14.The ink jet printer according to claim 11, further comprising: a powersupply wiring on the flexible substrate, the power supply wiringconnected to a power supply terminal of the drive circuit.
 15. The inkjet printer according to claim 11, wherein the common connection wiringis formed along a third edge of the flexible substrate that is alignedperpendicular to the first and second edges.
 16. The ink jet printeraccording to claim 15, further comprising: a dummy wiring on theflexible substrate, the dummy wiring disposed separately from the firstreference potential wiring and extending between the first and secondedges of the flexible substrate along a fourth edge of the flexiblesubstrate opposite the third edge.
 17. The ink jet printer according toclaim 16, wherein the dummy wiring is electrically isolated from anywiring on the head substrate and any wiring on the relay substrate. 18.The ink jet printer according to claim 16, wherein the common connectionwiring and the dummy wiring are disposed symmetrically with respect to acenter line of the flexible substrate extending between the first andsecond edges.
 19. The ink jet printer according to claim 16, furthercomprising: a power supply wiring on the flexible substrate has andhaving a portion extending between the dummy wiring and the firstreference potential wiring and being connected to a power supplyterminal of the drive circuit.
 20. The ink jet printer according toclaim 15, further comprising: a second common connection wiring on theflexible substrate, the second common connection wiring disposedseparately from the first reference potential wiring and extendingbetween the first and second edges of the flexible substrate along afourth edge of the flexible substrate opposite the third edge, thesecond common connection wiring being electrically connected to thecommon wiring and the second reference potential wiring.